Due to great potential application to flexible display devices etc., the organic light emitting diode (OLED) device is attached great importance by the scientific community and display industry in recent years, and it is one of the hot spots of current research and development.
However, the OLED device technology is currently experiencing a bottleneck in the development process; a main issue is that light emitting efficiency and lifetime of the OLED device cannot meet practical demand so as to greatly limit the development of the OLED technology. Factors of affecting the luminous efficiency and service life of the OLED device are multifaceted, but the fluorescence efficiency and stability of the light emitting material directly affect the performance of the OLED device. Most of dilute solutions of the light emitting materials have a high fluorescence quantum yield; however, they become weak fluorescence or not luminous in solid state. The phenomenon of the light emitting materials comes from aggregation caused quenching (ACQ). In general, the light emitting materials shall be used in solid thin film state; therefore, the ACQ effect inevitably occurs.
In order to reduce concentration of a light emitting material so as to resolve the ACQ effect, most of the light emitting materials are prepared with physically doping methods. There are many drawbacks in the physically doping methods, for example, to control the ratio between subject and object of the light emitting materials in the vacuum deposition process is difficult; phase separation exists between subject and object thereof; and processes of the physically doping method are complicated. If there is a light emitting material, the more it is aggregated, the stronger luminescence and the higher fluorescence quantum it yields, the ACQ effect would be possibly solved with the light emitting material. Such a light emitting material is called aggregation induced emission (AIE) material. Since 2001 Ben Zhong Tang et. al. reported that silacyclopentadiene derivatives (Silole) have the AIE effect, the AIE materials have been aroused great attention. With light emitting efficiency of the AIE materials in solid state being much better than light emitting efficiency thereof in solution state, a way to overcome the problem of doping organic light emitting materials is provided.
A fluorescence material doped with metal complex has a high light emitting efficiency with triplet state excitons in which green light material and red light material in the light emitting material can meet the demand of luminescence; however, the metal complex doped therein has specific structure of electrons so that blue light material therein cannot meet the demand of luminescence. Therefore, a thermally activated delayed fluorescence (TADF) material having properties between fluorescence and phosphorescence greatly increases light emitting efficiency of the fluorescence material, which is almost same as light emitting efficiency of a phosphorescence material, to make up shortage of the blue phosphorescent materials. Due to the ACQ effect existed in the known TADF material, an OLED device using the known TADF material can be only fabricated with the doping method. Therefore, it is one way of resolving the above said problems to develop a new light emitting material having the properties of the AIE material and the TADF material.